THIS invention relates to an apparatus and process for recovering a desired fraction of a raw material bearing the desired fraction.
A desired fraction from value bearing raw materials, such as rock, coal or the like is commonly recovered in a froth flotation method. In such a method, the raw material is typically ground into a finely particulate form which is then contacted with water and suitable flotation agents to form a slurry. The slurry is then contacted with finely dispersed gas bubbles rising through the slurry in such a way that the desired fraction is either selectively attached to the bubbles or is selectively left behind in the slurry. The appropriate phase be it the froth phase or the slurry, will then have a higher concentration of the desired fraction and may be separated for further processing.
A problem associated with conventional froth flotation methods is that the particulate material is not always in a form suitable for froth flotation. For instance, the surface of the particles may be covered with gangue material, be coated with an oxidised film or the like. As a result, the chemicals that are added to the slurry to impart hydrophobic tendencies to the particles to be floated are not able to operate optimally or at all.
According to a first aspect of the invention there is provided an apparatus for recovering a desired fraction of a raw material bearing the desired fraction, the apparatus comprising:
a vessel or cell defining a treatment chamber therein;
an inlet into the chamber for introducing a slurry of raw material to be treated into the chamber;
an attrition zone defined in a portion of the chamber proximate the inlet in the flow path of material introduced into the chamber, the particles being caused to impact against each other in the attrition zone to cause attritioning thereof;
a flotation zone defined in a distal portion of the chamber, in flow communication with the attrition zone, in which attritioned particles from the attrition zone can be contacted with gas bubbles to form a froth phase separated from the slurry by a slurry-froth interface such that the desired fraction is either selectively taken up into the froth phase by the gas bubbles or selectively left behind in the slurry; and
an outlet from the chamber for the froth phase.
The inlet preferably comprises multiple nozzles extending radially into the chamber and towards one another, the nozzles being arranged to introduce the slurry into the attrition zone in such a manner that the particles emanating from the different nozzles contact one another under high velocity.
Alternatively, or additionally, the attrition zone may have an associated attritioning means for causing the particles to contact one another under high velocity.
The attritioning means may, for instance, be in the form of a pair of spaced apart impellers defining the attrition zone between them, the impellers being arranged to force particles to collide with one another in the attrition zone.
The apparatus may include a screen or similar size selective component located intermediate the attrition zone and the flotation zone for selectively allowing attritioned particles to pass into the flotation zone.
The apparatus typically includes a bypass system for particles which have not been taken up into the froth phase to return to the attrition zone for a further pass.
The attrition zone is preferably located in a lower portion of the vessel and the flotation zone in an upper portion of the vessel.
The invention extends to a process for recovering a desired fraction from a raw material bearing the fraction, the process including the steps of:
(a) grinding the raw material into particles and contacting the particles with water to form a slurry;
(b) attritioning the particles by passing the slurry through an attrition zone in a suitable apparatus;
(c) contacting the attritioned particles with gas bubbles and suitable flotation agents in the same apparatus as in step (b) to form a froth phase separated from the slurry by a slurry-froth interface such that the desired fraction is either selectively taken up into the froth phase or selectively left behind in the slurry; and
(d) recovering the desired fraction from the froth phase or the slurry, as the case may be.